Gas pressure- generating cartridge



Jan. 1945- E. WHlTWO RTH ET AL 2,366,165

GAS PRESSURE-GENERATING CARTRIDGE Filed Oct. 18, 1939 u 9 8 v R 2 \2 2 \5 lllll s INVENTORS,

E [1w ar'ri XAZ'h-L'EwuPTh Thaw-L515 FI'HEIT'HEUT'L BY WM ATTORNEY.

Patented Jan. 2, 1945 r GAS PRESSURE-GENERATING CARTRIDGE Edward Whitworth, Saltcoats, and Thomas Thomson, Kilmarnock, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application October 18, 1939, Serial No. 300,068

In Great Britain October 18, 1938 Claims.

The present invention relates to the manufacture of gas-pressure-generating cartridges for the operation of gas-pressure-operated mechanical devices, and to charges for such cartridges. The invention relates particularly to cartridges for the operation of mechanical starters for internalcombustion engines and like devices, or for the direct starting of internal-combustion and other engines.

For the purposes mentioned, the operating pressure must be developed slowly at first so-that the inertia or resistance of the first mechanical parts to be moved is overcome and these parts set in motion at a very moderate speed so as to avoid damage to them, but subsequently the operating pressure must be developed at a considerably higher rate in order to accelerate the motion of the piston of the engine to some desired high speed notwithstanding the expansion caused by this motion. The gas-generating compositions used for such purposes obviously must be selfcombustible, and it is desirable that they should also be substantially ashless on combustion,

Various proposals have been made for the use of propellent explosives in the production of gas pressures for industrial purposes, but difficulty has been experienced in meeting these requirements. According to one proposal, an engine-starter cartridge is provided with a charge comprising a fuel consisting of a multiplicity of pellets of a propellent composition, and an igniting system adapted to produce gas in such small amounts and/or in so gradual a manner that the normal amount and rate of. pressure development of the ignited fuel is not appreciably increased thereby. The fuel may consist of a multiplicity of pellets of smokeless powder, in which case some of the pellets may have a greater number of perforations than others, and some may be of different compositions from others, whereby the rates of pressure development from the individual pellets are controlled so as to obtain the desired progressive burning of the fuel as a whole.

According to another proposal, an enginestarter cartridge is constructed to allow free venting of the combustion products of its charge and the charge comprises an igniting element and a propellent composition consisting of a relatively slow-burning deflagrating material such as a multiplicity of grains of colloided nitrocellulose powder. Such grains may be'formed so as to have different degrees of combustibility; e. g., some of the grains may have a greater number of perforations than others. Some or all of the grains may have incorporated in them a combus- .adapted to burn progressively with rapid evolution of gas and is so separated from the igniting means that its ignition is prevented until substantially complete combustion of the first section According to the present invention, a charge for a, gas-pressure-generating cartridge comprises a multiplicity of grains of a colloided nitrocellulose propellent powder, of which grains at least a substantial proportion has been surface-treated by combustion-moderating agents.

Our invention may be appreciated more readily by referring to the attached drawing, in which Figure 1 is a side view in cross-section of a preferred cartridge and Figure 2 is a detail view partly in perspective and partly in cross-section of granules of the propellent charge,

Similar numerals refer to similar parts throughout both views.

Referring in detail to Figure 1, a cartridge case 1, inside diameter 0.97", is provided with a fibre washer 2 fitting tightly in the bottom or base 3 of the case I. The fibre washer 2 carries an electric fuzehead 4, of which one lead 5 is connected to the brass base 3 of the cartridge case I, and the other lead 6 passes across a central hole 1 in the base 3 through which contact is made for firing. The fuzehead 4 is wrapped in a piece of sulphurless quickmatch, and lies among seven pellets 8,

0.26" long by 0.29" diameter, of a nitroglycerinecontaining propellent powder. The main propellent charge 9, placed on top of the igniting system consists of a mixture of 9.3 grams of uncoated nitrocellulose powder, in granules In, 0.29" long by 0.29" diameter, with 9.3 grams of the same powder whose granules II have been surface treated with 10 parts of dibutyl phthalate per parts of the untreated powder. A Celluloid disc I2 is placed over the powder and secured by the usual turnover l3.

Figure 2 is a detail view partly in perspective and partly in cross-section of uncoated granules l0 and granules II which have been surfacetreated with a dibutyl phthalate coating l 4.

The initial rate of gas evolution from a. surface-moderated solid rain is smaller than that from an untreated grain: but, as the eil'ect or the moderating agent does not persist during the combustion of the whole thickness of the grain, the time-rate of pressure development does not fall off so much during the progressive reduction of the burning surface as it would in the combustion of a grain of the same dimensions but having a uniform composition corresponding to that of the outer layers of the surface-moderated grain. Hence a fast-burning propellent powder may be used to develop pressure at a suitably high rate during the later stages of its combustion, and its time-rate of pressure-development during the early stages of'its combustion may be reduced to any desired extent by a suitable degree of surfacemoderation; e. g. by variation in the proportion of moderant applied to individual grains, and by variation in the proportion of moderated to unmoderated grains in the charge. Preferably this proportion is at least 1:1.

Any colloided nitrocellulose powder, whether' containing nitroglycerine or not, is suitable for use according to our invention; but we prefer to use. grain whose web-thickness is substantially greater than that of the grains commonly used as charges for cartridges for small arms.

For the purposes of the present invention, suitable surface-moderants for single-base nitrocellulose powders may be chosen from high-boiling gelatinisers for nitrocellulose, e. g. esters of carboxylic acids, alkyl or aryl ureas, or their mixtures. A double-base powder containing nitroglycerine may be treated for the purposes of the present invention by, for instance, the deposition of a coating of cellulose acetate on the surface of the grains, or by the use of the high-boiling gelatinisers already mentioned.

The following examples illustrate the invention.

A cartridge case, inside diameter 0.970 inch, is providedwith a fibre washer fitting tightly in the bottom of the case. The fibre washer carries an electric fuzehead, of which one lead is connected to the brass base of the cartridge case, and the other passes across a central hole in the base through which contact is made for firing. The fuzehead is wrapped in a piece of sulphurless quickmatch, and lies among '7 pellets, 0.26 long by 0.29" diameter, of a nitroglycerinecontaining propellent powder. The powder consists of nitroglycerine 30 parts, nitrocellulose 67 parts, ethyl centralite 1 part, potassium nitrate 2 parts and graphite 1 part, and approximately 3 grams of it are used. Thi combination of fuzemanner. 1000 grams of the powder are mixed for 5 minutes in a rotating copper bowl with enough water to form of the mixture. 100 grams of dibutyl phthalate are then sprayed on to the water-wet powder during rotation for 5 minutes more. The contents of the pan are raised gradually to 70 C. during 25 minutes, held at 70 C. for minutes, cooled to 45 C. in 15 minutes and then steeped in water at 55 C. for 24 hours. The steeped powder is then stoved at 43 C. for 24 hours, and finally graphited with graphite.

head, quickmatch and powder makes up the igniting system of the cartridge.

The main propellent charge, placed on top 0 the igniting system, consists of a mixture of 9.3 grams of uncoated nitrocellulose powder, in granules 0.29" long by 0.29" diameter, with 9.3 grams of the same powder whose granules have been surface-treated with 10 parts of dibutyl phthalate per 100 parts of the untreated powder. A Celluloid disc is placed over the powder and secured by the usual turnover. The completed cartridge is about 2 inches long.

The composition of the untreated powder is 100 parts nitrocellulose and 1 part diphenylamine, and the nitrocellulose is colloided in the usual manner with ether-alcohol.

The surface-treatment of the moderated portion of the charge is carried out in the following When fired in a closed vessel of 1260 cc. capacity, the cartridge produces a pressure of lbs. per square inch in 0.25 second, and a maximum pressure of 1250 lbs. per square inch in 0.5 second. A similar cartridge charged with unmodified powder produces a pressure of 170 lbs. per square inch in 0.10 second, and a maximum pressure of 1250 lbs. per square inch in 0.25 second.

Example 2 A cartridge is constructed and charged as described in Example 1, except that the powder portion of the igniting system consists of 7 pellets of powder, 0.30" long and 0.21" diameter.

consisting of nitrocellulose.l00 parts, diphenyl-' amine 1 part, graphite 5 parts, potassium nitrate 3 parts and barium nitrate 10 parts, and collolded in the usual way with ether alcohol.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as de-- fined in the appended claims.

We claim:

1. A gas-pressure-generating cartridge for the operation of a gas-pressure-operated mechanical device, wherein the gas producing charge comprises a multiplicity of grains of a colloided nitrocellulose propellent powder having a length of about 0.29" and a diameter of about 0.29", substantially one-half of said grains being uncoated and substantially one-half of said grains having been surface-treated by application thereto oi about 10%, based upon the weight of the grains prior to surface-treatment, of dibutyl phthalate.

2. A gas-pressure-generating cartridge for the operation of a gas-pressure-operated mechanical device, wherein the gas producing charge comprises a multiplicity of grains of a colloided nitrocellulose propellent powder having a length of about 0.29" and a diameter of about 0.29", substantially one-half of said grains being uncoated and substantially one-half of said grains having been surface-treated by application thereto of dibutyl phthalate.

3. A gas-pressure-generating cartridge for the operation of a gas-pressure-operated mechanical device, wherein the gas producing charge comprises a multiplicity of grains of a colloided nitrocellulose propellent powder having a length of about 0.29 and a diameter of about 0.29", substantially one-half of said grains being uncoated and substantially one-half of said grains having been surface-treated by application thereto of an ester of a carboxylic acid.

4. A gas-pressure-generating cartridge for the operation of a gas-pressure-operated mechanical device, wherein the gas producing charge comprises a multiplicity of grains of a colloided nitrocellulose propellent powder having a length of about 0.29" and a diameter of about 0.29", at

cellulose propellent powder having a length of about 0.29" and a diameter of about 0.29", a substantial proportion of said grains having been surface-treated by application thereto of a combustion-moderating agent which is a high boiling gelatinizer for nitrocellulose selected from the group consisting of esters of carboxylic acids,

alkyl ureas, aryl ureas, and mixtures of esters of carboxylic acids, alkyl ureas and aryl ureas.

EDWARD WHITWOR'IH. THOMAS THOMSON. 

